LTC2955ITS8-2#TRMPBF 数据手册
LTC2955
Pushbutton On/Off
Controller with Automatic
Turn-On
Description
Features
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Automatic Turn-On Via Voltage Monitor Input
Wide Input Supply Range: 1.5V to 36V
Low Supply Current: 1.2µA
±25kV ESD HBM on PB Input
±36V Wide Input Voltage for PB Input
Low Leakage EN Output Allows DC/DC Converter
Control (LTC2955-1)
High Voltage EN Output Drives External P-Channel
MOSFET (LTC2955-2)
Simple Interface Allows Graceful µP Shutdown
Adjustable Turn-Off Timer
10-Lead 3mm × 2mm DFN and 8-Lead ThinSOT™
Packages
The LTC®2955 is a micropower, pushbutton on/off controller that manages system power by generating a clean enable
output from the supply monitor input and the debounced
pushbutton input. It features an interrupt output that
notifies the system of a pushbutton or low supply event.
When the system is ready, it may use the power kill input
to shut off power. If the pushbutton remains pressed for
more than the configurable turn-off duration, the system
power is forced off.
The supply input covers a wide range from 1.5V to 36V.
The robust pushbutton input handles wide voltage swings
of ±36V and ESD strikes to ±25kV (human body model)
without latchup or damage. A low 1.2µA supply current
maximizes battery run time. Separate versions are available for positive or negative enable polarities.
Applications
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L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT and PowerPath are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Desktop and Notebook Computers
GPS Devices
Portable Instruments
Automotive Electronics
Typical Application
Automatic Turn-On with Power-Fail Indication
VTRIP = 5.4V
LT3008-3.3
VOUT
VIN
8.4V
Pushbutton On/Off with Interrupt
TURN ON PULSE
3.3V
VIN
2.32M
402k
1M
EN
R7
1M
EN
LTC2955DDB-1
SEL
INT
ON
PB
TMR GND
LONG PULSE
PB
SHDN
0.1µF
SHORT PULSE
KILL
TURNS ON
STAYS ON
TURNS OFF
µP
INT
PGD
INTERRUPT
POWER-FAIL
INTERRUPT
2955 TA01b
2955 TA01a
2955fa
For more information www.linear.com/LTC2955
1
LTC2955
Absolute Maximum Ratings
(Note 1)
VIN.............................................................. –0.3V to 40V
Input Voltages
PB............................................................ –40V to 40V
ON.......................................................... –0.3V to 40V
SEL......................................................... –0.3V to 40V
KILL.......................................................... –0.3V to 6V
Output Voltages
EN/EN..................................................... –0.3V to 40V
INT............................................................ –0.3V to 6V
PGD.......................................................... –0.3V to 6V
TMR....................................................... –0.3V to 2.7V
Operating Temperature Range
LTC2955C................................................. 0°C to 70°C
LTC2955I..............................................–40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
TSOT-23 Package.............................................. 300°C
Pin Configuration
TOP VIEW
INT 1
9
KILL
8
TMR
VIN 4
7
SEL
PB 5
6
GND
*EN/EN 3
TOP VIEW
10 ON
PGD 2
11
ON
KILL
TMR
GND
8
7
6
5
INT
EN/EN*
VIN
PB
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 195°C/W
*PIN 7 IS EN FOR LTC2955-1
AND IS EN FOR LTC2955-2
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 55°C/W
EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL
*PIN 3 IS EN FOR LTC2955-1
AND IS EN FOR LTC2955-2
Order Information
1
2
3
4
(http://www.linear.com/product/LTC2955#orderinfo)
Lead Free Finish
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2955CDDB-1#TRMPBF
LTC2955CDDB-1#TRPBF
LGBJ
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2955CDDB-2#TRMPBF
LTC2955CDDB-2#TRPBF
LGBM
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2955IDDB-1#TRMPBF
LTC2955IDDB-1#TRPBF
LGBJ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2955IDDB-2#TRMPBF
LTC2955IDDB-2#TRPBF
LGBM
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2955CTS8-1#TRMPBF
LTC2955CTS8-1#TRPBF
LTGBK
8-Lead Plastic TSOT-23
0°C to 70°C
LTC2955CTS8-2#TRMPBF
LTC2955CTS8-2#TRPBF
LTGBN
8-Lead Plastic TSOT-23
0°C to 70°C
LTC2955ITS8-1#TRMPBF
LTC2955ITS8-1#TRPBF
LTGBK
8-Lead Plastic TSOT-23
–40°C to 85°C
LTC2955ITS8-2#TRMPBF
LTC2955ITS8-2#TRPBF
LTGBN
8-Lead Plastic TSOT-23
–40°C to 85°C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
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2955fa
For more information www.linear.com/LTC2955
LTC2955
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply
VIN
Supply Voltage Range
l
1.5
IIN
VIN Supply Current
l
0.5
VUVL
VIN Undervoltage Lockout
l
VUVL(HYST)
VIN Undervoltage Lockout Hysteresis
l
VPB(MIN(MAX))
PB Voltage Range
l
–36
VPB
PB Input Threshold
PB Falling
l
0.6
VPB(HYST)
PB Input Threshold Hysteresis (Note 3)
VPB(VOC)
PB Open Circuit Voltage
I = –1µA
l
IPB
PB Input Leakage Current
6V < PB < 36V
PB = 1V
PB = –36V
l
l
l
VON
ON Threshold
ON Rising
l
VON(HYST)
ON Hysteresis
DFN Package Only
ION
ON Input Leakage Current
ON = 1V
ON = 36V
l
l
VKILL
KILL Input Threshold Voltage
KILL Falling
l
VKILL(HYST)
KILL Input Threshold Hysteresis (Note 3)
IKILL
KILL Input Leakage Current
VSEL
SEL Input Threshold
ISEL
SEL Input Current
SEL = 1V
SEL = 36V
l
l
VEN/EN(VOL)
EN/EN Voltage Output Low
I = 1mA
l
1.5
VIN Rising
36
V
1.2
3
µA
1.0
1.15
1.3
V
30
85
200
mV
36
V
1
V
Input Pins
0.8
40
3.0
mV
4.3
5.5
V
–1
–4
±10
–8
–400
µA
µA
µA
0.76
0.80
0.84
V
40
mV
±10
±100
0.76
0.80
0.84
30
KILL = 1V
l
l
0.4
0.8
nA
nA
V
mV
±50
nA
1.2
V
±50
±100
nA
nA
0.4
V
Output Pins
0.175
VEN(VOH)
EN Voltage Output High (LTC2955-1)
I = 0µA, –0.5µA
l
VEN(VOH)
EN Voltage Output High (LTC2955-2)
I = 0µA, –0.5µA
l
VIN – 1.5
5.5
V
IEN
EN Pull-Up Current (LTC2955-1)
EN = 0V
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–1.2
–2
–2.8
µA
IEN
EN Pull-Up Resistance (LTC2955-2)
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0.45
0.9
1.35
MΩ
VINT(VOL)
INT Voltage Output Low
I = 3mA
l
0.4
V
±50
nA
5.5
V
0.4
V
V
IINT
INT Leakage Current
INT = 5V
l
VPGD(VOH)
PGD Voltage Output High
I = 0µA, –0.5µA
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VPGD(VOL)
PGD Voltage Output Low
I = 3mA
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IPGD
PGD Pull-Up Current
PGD = 0V
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–1.2
–2
–2.8
µA
ITMR(PU)
TMR Pull-Up Current
TMR = 0V
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–2
–3
–4
µA
ITMR(PD)
TMR Pull-Down Current
TMR = 1.5V
l
2
3
4
µA
1.5
2955fa
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3
LTC2955
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
tDB(ON)
PB, ON Turn-On Debounce Time
PB Falling or ON Rising → Enable Asserted
tDB(OFF)
PB Interrupt Debounce Time
tTMR
UNITS
l
19
32
45
ms
PB Falling → INT Falling
l
19
32
45
ms
Additional Turn-Off Debounce Time
CTMR = 2200pF
l
5.8
11.5
17.2
ms
tINT(MIN)
Minimum INT Pulse Width
INT Falling → TMR Rising
l
19
32
45
ms
Timing
tON(PD)
ON Interrupt Delay
ON Falling → INT Falling, VSEL > 0.8V
l
200
µs
tPGD(PD)
PGD Propagation Delay
ON Falling → PGD Falling
l
200
µs
tKILL(PD)
KILL Propagation Delay
KILL Falling → Enable Released
l
60
µs
tKILL(PW)
KILL Minimum Pulse Width
l
60
µs
tKILL(ON BLANK) KILL Turn-On Blanking (Note 4)
KILL Low, Enable Asserted → Enable
Released
l
304
512
720
ms
tEN(LOCK OUT)
Enable Released → Enable Asserted
l
0.6
1
1.4
s
EN/EN Lockout Time (Note 5)
Note 4: The KILL turn-on blanking time is the waiting period immediately
after the enable output is asserted. This blanking time allows sufficient
time for the regulator and the µP to perform power-up tasks. The KILL, PB,
and ON inputs are ignored during this period.
Note 5: The enable lockout time is the waiting period immediately after the
enable output is released. It allows an application to properly power-down
such that the next power-up sequence starts from a consistent powered
down configuration. PB and ON are ignored during this period.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 3: Guaranteed by design, not subject to test.
Typical Performance Characteristics
Supply Current vs Temperature
VIN = 7V, TA = 25°C, unless otherwise noted.
Undervoltage Lockout vs
Temperature
Supply Current vs Supply Voltage
1.6
1.6
1.20
1.4
1.18
1.2
1.16
1.3
IVIN (µA)
IVIN (µA)
1.4
1.2
1.1
1.0
VUVL (V)
1.5
1.0
0.8
0.8
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
2955 G01
4
0.6
1.12
TA = –40°C
TA = 25°C
TA = 85°C
0.9
0
5
10
15
20 25
VIN (V)
30
35
1.14
40
2955 G02
1.10
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
2955 G03
2955fa
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LTC2955
Typical Performance Characteristics
ON/KILL Threshold vs
Temperature
VIN = 7V, TA = 25°C, unless otherwise noted.
Turn-On Debounce Time
vs Temperature
0.810
Additional Turn-Off Debounce
Time vs TMR External Capacitance
36
10000
35
0.805
1000
0.800
tTMR (ms)
tDB(ON) (ms)
VON/KILL (V)
34
33
100
32
0.795
10
31
0.790
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
30
–50
125
–25
50
25
0
75
TEMPERATURE (°C)
2955 G04
–3.4
5.0
–3.3
4.8
10
100
TMR EXTERNAL CAPACITANCE (nF)
1000
EN Output High Voltage vs Supply
Voltage
5.0
4.0
–3.1
–3.0
–2.9
VEN(VOH) (V)
4.6
VEN(VOH) (V)
ITMR(PU) (µA)
1
2955 G06
EN Output High Voltage vs
Temperature
–3.2
4.4
4.2
3.0
2.0
4.0
–2.8
1.0
3.8
–2.7
–2.6
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
3.6
–50
125
–25
50
25
0
75
TEMPERATURE (°C)
2955 G07
VIN = 1.5V
IPB (µA)
250
200
50
–50
–200
300
–160
250
–120
200
–80
–25
50
25
0
75
TEMPERATURE (°C)
100
125
2955 G10
3
4
VIN (V)
6
5
40
–40
–20
40
0
20
PB VOLTAGE (V)
7
150
100
50
0
100
2
PB Voltage vs External PB
Resistance to Ground
–40
VIN = 7V
150
1
2955 G09
PB VOLTAGE (mV)
400
300
0.0
125
PB Input Current vs PB Voltage
I = 1mA
350
100
TA = –40°C
TA = 25°C
TA = 85°C
2955 G08
EN/EN Output Low Voltage vs
Temperature
VEN/EN(VOL) (mV)
1
125
2955 G05
TMR Pull-Up Current
vs Temperature
450
100
2955 G11
0
TA = –40°C
TA = 25°C
TA = 85°C
50
20
0
10
30
40
EXTERNAL PB RESISTANCE TO GROUND (kΩ)
2955 G12
2955fa
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5
LTC2955
Pin Functions
EN: Enable Output (LTC2955-1). EN is an active high output
to control the turn-on/off of the system power. Connect this
pin to the RUN or SHUTDOWN pin of the voltage regulator.
The LTC2955 asserts EN high when the pushbutton is
pressed or when ON goes high. The output high voltage
follows the internal LDO output which provides sufficient
margin for most SHUTDOWN pin thresholds.
EN: Inverted Enable Output (LTC2955-2). EN is an active
low output to control the turn-on/off of the system power.
It may drive a voltage regulator’s active low enable input,
or it may drive the gate of a P-channel MOSFET. In the
turn-off state, the LTC2955 pulls this pin to VIN through
an internal 900k resistor. The LTC2955 pulls EN to GND
when the pushbutton is pressed or when ON goes high.
Exposed Pad (DFN only): Exposed pad. Leave open or
connect to device ground.
GND: Device Ground.
INT: Open Drain Interrupt Output. Connect this pin to the
interrupt input of the system with a pull-up resistor to the
system supply. The LTC2955 asserts the INT pin low when
it receives the turn-off command from the pushbutton or
the ON pin. The minimum pulse width of the INT signal is
32ms and can be extended through the TMR pin.
KILL: Kill Input. A low at KILL releases the enable output
(EN/EN). This pin can be driven by the microprocessor or it
can be used as a voltage monitor input. Tie to the system
power supply or an external voltage of 1.2V~5V if unused.
ON: Monitor Input. Connect this pin to an external resistive
divider from the monitored voltage. This allows automatic
system turn-on when the monitored voltage transitions
high. For the DFN part, if the SEL pin is tied high, it also
allows automatic system turn-off when the monitored
voltage transitions low. Tie to GND if unused.
PB: Pushbutton Input. This is an active low input with a
900k pull-up to an internal LDO. Connect one terminal of
the pushbutton to this pin and connect the other terminal of
the pushbutton to GND. The pin may be left open if unused.
PGD (DFN only): ON Status Output. A high on this pin
indicates that the voltage at the ON pin is above the input
threshold of 0.8V. This pin can be used as a system input
to inform the system whether the turn-on was triggered by
the ON pin or the pushbutton pin. Leave open if unused.
SEL (DFN only): Mode Select Input. Connect SEL to GND
to block the ON pin falling edge from activating system
turn-off. Connect SEL to VIN to allow both the ON pin rising
and falling edges to activate system turn-on and turn-off
respectively. For the TSOT package, SEL is internally tied
to GND. Do not leave open.
TMR: Timer Pin. A capacitor to ground determines the
additional time (5.2 seconds/μF) beyond the default 64ms
that the pushbutton must be held low before immediately
releasing the EN/EN and INT outputs. The turn-off debounce
time defaults to 64ms if this pin is left open. To disable the
ability to force a system power-down with a pushbutton
press, ground the TMR pin.
VIN: Power Supply Input. For > 20V applications, connect
VIN to the power source through a 1k resistor and bypass
VIN to GND with a 10nF low ESR capacitor.
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2955fa
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LTC2955
Block Diagram
VIN
900k
EN
(2955-2)
VLDO
EN CONTROL
2µA
LTC2955-2
VIN
REGULATOR
VLDO ≈ 5.2V
EN
(2955-1)
EN CONTROL
VLDO
900k
PB
0.8V
EN CONTROL
–
VLDO
LOGIC
2µA
DEBOUNCE
+
OSCILLATOR
ON
ON
LTC2955-1
OSCILLATOR
f = 1kHz
PGD*
+
OFF
0.8V
INT
–
+
GND
TMR
+
SEL*
–
–
0.8V
KILL
0.8V
2955 BD
*DFN ONLY
2955fa
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7
LTC2955
Operation
Overview
The LTC2955 is a pushbutton on/off controller that manages system power based on a pushbutton input (PB pin)
and a voltage monitor input (ON pin). In a typical application,
the enable output (EN/EN) turns on system power when
the pushbutton is pressed or the supply monitor detects
the presence of a primary or secondary supply such as a
wall adaptor or car battery.
After the system is powered up, a pushbutton event asserts the interrupt output (INT) which can be used in menu
driven applications to request for a system power-down.
A power kill input (KILL) allows a microprocessor or system to release the enable output immediately, effectively
powering down the system. System power is also forced
off if the pushbutton remains asserted for more than the
forced turn-off activation time configurable via the TMR pin.
The LTC2955 is also designed with a blanking time after
each system turn on and off event. During this blanking
time, the LTC2955 ignores the KILL, ON and PB pins,
thus ensuring that the system stays on/off for a minimum
amount of time. This provides sufficient time for the voltage
regulator to turn on/off and allows it to charge/discharge
its output to the final voltage. It also allows the µP sufficient time to perform power on/off tasks.
The PGD output indicates the status of the ON pin to allow
the system to differentiate between pushbutton turn-on
or supply plug-in events.
Turn-On Sequence and KILL Blanking Time
The LTC2955-1 asserts the EN output high if the pushbutton is pressed or the ON pin goes high. This is typically
used to turn on a DC/DC converter or linear regulator.
Figure 1 shows the turn-on sequence of the LTC2955-1
initiated by the PB pin. When the button is pressed at time
t1, a high to low transition on the PB pin initiates the turnon sequence. The PB pin must stay low continuously for
a period of 32ms (tDB(ON)) before the LTC2955-1 asserts
the EN output high. Once EN goes high (t2), an internal
512ms blanking time (t KILL(OnBlank)) is started. During
this blanking time, the LTC2955-1 ignores the KILL, ON
and PB pins and keeps EN high for at least 512ms. This
provides sufficient time for the voltage regulator to turn
on and charge its output to the final voltage and allows
the µP enough time to perform power on tasks. The µP
must pull the KILL pin high during this 512ms blanking
time, or else EN will go low at the end of this time (t3).
t2
t1
t3
PB AND KILL IGNORED
PB
tDB(ON)
tKILL(ON BLANK)
EN
(LTC2955-1)
2955 F01
Figure 1. Pushbutton Turn-On Timing
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LTC2955
Operation
A high to low transition on PB (t1) starts the turn-off
sequence. In order to assert INT (interrupt output) low,
PB must stay low continuously for 32ms (tDB(OFF)). At
the end of the 32ms (t2), the INT pin is asserted low and
will stay low for at least 32ms (tINT(MIN)), even if the PB
pin goes high during this period (t2 to t4). When the µP
receives this interrupt signal, it should start to perform
its power-down functions and assert KILL low (t3) once
it is done. The LTC2955-1 will then release INT and pull
EN low, thus turning off the system power, as shown with
dotted lines in Figure 3.
At the end of this blanking time, the LTC2955-1 will check
that the PB pin is high. If the PB pin remains low, it will be
ignored until a high is detected on the pin. The next low
on the PB pin will initiate a turn-off sequence.
Figure 2 shows a similar LTC2955-1 turn-on sequence
with the ON pin going high. The timing sequence is very
similar to that initiated by the pushbutton. The PGD output
follows the ON pin.
PB Pin Turn-Off Sequence
Figure 3 shows the turn-off sequence of the LTC2955-1
initiated through the PB pin. A turn-off sequence refers
to the LTC2955-1 releasing the EN output. This turns off
the voltage regulator.
The user can also force the system to power-down if the
µP fails to respond to the interrupt signal (KILL pin remains
t2
t1
t3
ON AND KILL IGNORED
ON
tKILL(ON BLANK)
tDB(ON)
EN
(LTC2955-1)
PGD
2955 F02
Figure 2.ON Pin Turn-On Timing
t1
t2
t3
t4
t5
t6
PB
IGNORED
PB
t7
PB
IGNORED
tDB(OFF)
tEN(LOCKOUT)
IGNORED
KILL
16 CYCLES
TMR
tTMR
INT
tINT(MIN)
EN
(LTC2955-1)
2955 F03
Figure 3. Pushbutton Turn-Off Timing
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9
LTC2955
Operation
high). This can be done by holding the pushbutton down
for a long period (> tDB(OFF) + tINT(MIN) + tTMR) as shown
with the solid lines in Figure 3. If the PB pin remains low at
the end of the 32ms minimum INT pulse width (tINT(MIN)),
the external timer will start counting (t4).
The capacitance at the TMR pin determines the duration
of this timer and it will count for 16 cycles (tTMR). If the
PB pin remains low at the end of the 16 cycles (t5), the
LTC2955-1 will force the EN pin low and the INT pin high.
See Applications Information for adjusting tTMR.
After the EN output goes low and the PB pin goes high,
the LTC2955-1 starts the one second lockout time
(tEN(LOCKOUT)). During this lockout time (t6 to t7 in Figure 3)
the PB and ON inputs are ignored. This is to allow time for
the voltage regulator to turn off and for its output to decay
to 0V. This ensures that the µP has completely powered
down before it is allowed to restart. After the one second
lockout time, the LTC2955-1 proceeds to the next stage
to wait for a turn-on command and the cycle will repeat
as above. If the PB pin remains low after the EN output
goes low, the LTC2955-1 will delay the start of this lockout
time until the PB pin goes high.
If the PB pin goes high when the external timer is still
counting, as shown in Figure 4, the turn-off sequence will
be aborted. The INT pin is forced high immediately and
the EN pin remains high.
PB IGNORED
PB
tDB(OFF)
t < tTMR
TMR
INT
2955 F04
tINT(MIN)
Figure 4. Pushbutton Turn-Off Aborted
10
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LTC2955
Operation
ON Pin Turn-Off Sequence (DFN Package Only)
to perform power-down functions. The INT pin will stay
low for at least 32ms (tINT(MIN)). When the µP receives
this interrupt signal, it should start to perform its powerdown functions and assert the KILL input low (t2) once it
is done. The LTC2955-1 will then release the EN and INT
outputs, thus turning off the system power, as shown with
dotted lines in Figure 5.
Figure 5 shows the turn-off sequence of the LTC2955-1
initiated by the ON pin. The timing sequence is slightly
different from that by the pushbutton as there is no debounce time (tDB(OFF)) before the INT pin pulls low. The
ON pin falling edge can start the turn-off sequence only
if the following two conditions are met: (1) The preceding
turn-on sequence was initiated by the ON pin rising edge,
and (2) The SEL pin must be tied high (>0.8V). For TS8
package, the ON pin falling edge is ignored.
If the µP fails to respond (KILL pin remains high, as shown
with solid line in Figure 5) and the ON pin remains low 32ms
after INT goes low, the external timer will start counting
for 16 cycles (tTMR, t3 to t4). If the ON pin remains low
at the end of the 16 cycles (t4), the LTC2955-1 will force
the EN pin low and the INT pin high. See Applications
Information for adjusting tTMR.
In Figure 5, a high to low transition at ON (t1) starts the
turn-off sequence. The interrupt output (INT) is asserted
immediately when the ON pin goes low. Unlike the PB
pin turn-off sequence, there is no 32ms debounce time
(tDB(FF)) for the ON pin going low. This allows the system
to initiate a shutdown as soon as the monitored supply is
removed and allows the µP the maximum amount of time
t1
After the EN output goes low, the LTC2955-1 starts the
one second lockout time (tEN(LOCKOUT)). During this lockout
time (t4 to t5), the PB and ON inputs are ignored.
t2
t3
t4
t5
IGNORED
ON
tINT(MIN)
IGNORED
KILL
16 CYCLES
TMR
tTMR
INT
tEN(LOCKOUT)
EN
(LTC2955-1)
PGD
2955 F05
Figure 5. ON Pin Turn-Off Timing (DFN Only, VSEL > 1.2V and the Preceding Turn-On Sequence Was
Initiated by the ON Pin Rising Edge
2955fa
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11
LTC2955
Operation
PB vs ON Pin
With the DFN package, if the turn-on sequence is initiated by the pushbutton, the ON input is ignored until the
pushbutton is pressed again to initiate a turn-off sequence.
As shown in Figure 6, the PB pin initiates a turn-on sequence
at time t1 before the ON pin goes high at time t2. Once EN
goes high (t3), the ON input is ignored, so a falling edge
at the ON pin (t4) will not initiate a turn-off sequence even
if the SEL pin is high. This allows the system to remain
powered up if it is plugged in and out of a secondary power
source while the system is already turned on.
If the turn-on sequence is initiated by the ON pin, both
the pushbutton and the ON pin falling edge can initiate
the turn-off sequence. For the TS8 package, ON pin falling
edge is always ignored regardless of which pins initiate
the turn-on.
The PB pin has priority over the ON pin, so if the PB pin
goes low and ON pin goes high at the same time, the
LTC2955-1 will monitor the PB pin for the 32ms debounce
time and ignore the ON pin unless the PB pin bounces
during the 32ms.
ON Pin Initial Turn-On
If the LTC2955-1 powers up with the ON pin already high,
the EN pin will go high after a power-up delay of about
one second. Subsequently, if the pushbutton is pressed
to force EN low, the LTC2955-1 will not initiate another
turn-on even if the ON pin remains high. The LTC2955-1
needs a rising edge at the ON pin or a falling edge on the
PB pin to initiate the subsequent turn-on.
ON PIN IS IGNORED, SINCE
PUSHBUTTON IS PRESSED
FIRST
t1
t2
ON GOING LOW IS IGNORED,
SINCE THE EN IS ASSERTED
BY THE PUSHBUTTON
t3
t4
t5
ON PIN
PB PIN
PGD PIN
TURN-ON BY PB
EN PIN
2955 F06
Figure 6. Pushbutton Is Pressed Before the ON Pin Goes High
12
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LTC2955
Operation
As shown in Figure 7, if the ON pin is high when power is
first applied to the LTC2955-1 at time t1, the EN pin will
go high (at t2) after the one second EN lockout time. At
time t3, the pushbutton is pressed to activate turn-off
while the ON pin remains high. The LTC2955-1 will wait
for a rising edge at the ON pin or a low at the PB pin to
activate the next turn-on. As shown at time t4, after the
one second lockout time, the EN stays low with ON high.
At time t5, only the rising edge of the ON pin or a PB event
will trigger the next turn-on again.
LTC2955-1, LTC2955-2 Versions
The LTC2955-1 and LTC2955-2 differ only by the polarity
of the high voltage (36V absolute maximum) enable pin.
The LTC2955-1 EN pin is a high true output designed to
drive the SHUTDOWN pin of most voltage regulators. In
turn-on mode, this pin is pulled high by a pull-up current of
2µA powered by an internal LDO, which gives a high level
output voltage (VOH) of typically 4.3V. In turn-off mode,
this pin is pulled low by an internal N-channel MOSFET. If
a higher VOH or higher pull-up current is required, connect
the EN pin to an external source through a pull-up resistor.
The LTC2955-2 EN pin is a low true enable output designed
to drive the gate of an external P-channel MOSFET. In
turn-on mode, the EN pin is pulled low by an internal
N-channel MOSFET. In turn-off mode, this pin is pulled
high to VIN through an internal 900k resistor. An external
pull-up resistor can be connected between this pin and
VIN to increase the pull-up current.
POWER FIRST APPLIED TO
LTC2955 VIN PIN
t1
t2
VIN
t3
t4
A HIGH AT ON PIN IS IGNORED AFTER
THE FIRST TURN-ON/OFF SEQUENCE
t5
ON RISING EDGE
ON PIN
TURN-OFF BY
PUSHBUTTON
PB PIN
TURN-ON BY ON
HIGH LEVEL
TURN-ON BY ON
RISING EDGE
EN PIN
2955 F07
tEN(LOCKOUT)
tEN(LOCKOUT)
Figure 7. Power First Applied to LTC2955-1
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13
LTC2955
Applications Information
Adjusting the Forced Turn-Off Timing
Voltage Monitoring with KILL Input
The LTC2955 allows the user to force the system power to
turn off if the µP fails to respond during fault conditions. As
shown by the solid lines in Figure 3 and Figure 5, when the
µP fails to bring the KILL pin low after the interrupt signal
is asserted, the user can force a turn-off by holding down
the pushbutton. The length of time that PB must be held
low is given by a fixed 64ms delay (tDB(OFF) + tINT(MIN))
plus an adjustable power-down timer delay (tTMR). The
adjustable delay is set by placing an optional external
capacitor on the TMR pin. Use the following equation to
calculate the capacitance for the desired delay. CTMR is
the external capacitor at the TMR pin:
The KILL pin can also be used as a voltage monitor input.
Figure 8 shows an application where the KILL pin has a dual
function. It is driven by a low leakage open drain output
of the µP. It is also connected to a resistive divider that
monitors battery voltage (VIN). When the battery voltage
falls below the set value, the voltage at the KILL pin falls
below 0.8V and the EN pin is quickly pulled low. Note that
the resistor values should be as large as possible, but
small enough to keep leakage currents from tripping the
0.8V KILL comparator.
CTMR = 0.19 • tTMR [µF/sec]
If there is no circuitry available to drive the KILL pin,
this pin can be connected to a voltage regulator output
through a resistive divider or RC network as shown in
Figure 9. The KILL pin acts as a voltage monitor pin that
shuts down the regulator when its output voltage drops
below a certain level.
As an example, if the required turn-off debounce time is
one second:
tTMR = (1000ms – 64ms)
CTMR = 0.19 • 0.936
Required CTMR is 0.178µF
The ON pin turn-off debounce time is 32ms less than the
PB pin debounce time since there is no tDB(OFF). If the
TMR pin is left open, the turn-off debounce time defaults
to 64ms for the PB pin and 32ms for the ON pin.
Operation Without µP
The minimum pulse width needed to trigger KILL is 30µs.
If there are glitches on the resistor pull-up voltage that
are wider than 30µs and transition below 0.8V, then an
appropriate bypass capacitor should be connected to the
KILL pin.
VIN = 9V
VIN = 9V
VIN
VIN
VOUT
LT3060
R3
583k
1%
VOUT
VOUT
LT3060
VOUT
SHDN
SHDN
R1
10k
R2
100k
1%
C4
0.1µF
EN
VIN
LTC2955TS8-1
INT
PB
ON
INT
µP
KILL
(OPEN DRAIN)
KILL
GND
C4
0.1µF
R1
10k
TMR
EN
VIN
LTC2955TS8-1
INT
PB
KILL
ON
GND
+
TMR
CTMR*
1µF
*OPTIONAL
2955 F08
CTMR*
1µF
*OPTIONAL
C3*
0.01µF
2955 F09
Figure 9. Application without µP
Figure 8. Input Voltage Monitoring with KILL Input
14
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LTC2955
APPLICATIONS INFORMATION
High Voltage PowerPath™ Switching
capacitor at the pin lessens the impact of this coupling.
The parasitic series inductance may cause unpredictable
ringing at the PB pin; placing a 5.1k resistor from the PB
pin to the pushbutton switch reduces this ringing. Figure 11
shows an example of this RC network at the PB pin.
The high voltage EN open drain output of the LTC2955-2
is designed to switch on/off an external power P-channel
MOSFET. This allows a user to connect/disconnect a power
supply (or battery) to its load by toggling the PB pin. Figure 10
shows the LTC2955-2 controlling a two cell Li-Ion battery
application. The KILL pin is connected to the output of the
external MOSFET through a resistive divider. The KILL pin
serves as a voltage monitor. When VOUT drops below 6V,
the EN pin is pulled high (to VIN) after 15µs later. R9 slows
down the turning on of M1 so as to limit the inrush current
when M1 turns on to charge up the capacitor at VOUT. R5
helps to speed up the turning off of M1 and also to keep
M1 off when the input voltage rise time is fast.
External Pull-Up Resistor on PB Pin
An internal 900k pull-up resistor on the PB pin makes an
external pull-up resistor unnecessary. Leakage current on
the PB board trace, however, will affect the open circuit
voltage on the PB pin. If the leakage is too large (>1µA),
the PB voltage may fall close to the threshold window. To
VIN
PARASITICS
TRACE
CAPACITANCE
PB Pin in a Noisy Environment
The rugged PB pin is designed to operate in noisy environments. Transients below ground and above VIN (–36V <
VIN < 36V) will not damage the rugged PB pin. Additionally,
the PB pin can withstand ESD HBM strikes of up to ±25kV.
VIN
R6
5.1k
PB
NOISE
C5
0.1µF
TRACE
INDUCTANCE
+
4.2V
SINGLE CELL
Li-ION BATTERY
R9
100k
VOUT
PB
KILL
GND
VOUT,TRIP POINT = 6V
R1
649k
1%
EN
VIN
LTC2955TS8-2
INT
ON
TMR
Figure 11. Noisy PB Trace
R5*
100k
C4
0.1µF
KILL
GND
DETAILS OMITTED
FOR CLARITY
M1
4.2V
SINGLE CELL
Li-ION BATTERY
INT
2955 F11
However, if the pushbutton switch is located physically far
from the LTC2955 PB pin, the parasitic capacitance and
parasitic series inductance of the connecting cable or PCB
trace can create problems. The parasitic capacitance can
couple external noise onto the PB input; placing a 0.1µF
+
EN
LTC2955-1
VTH = 0.8V INPUT
TMR
CTMR*
0.033µF
OPTIONAL GLITCH
FILTER CAPACITOR
R4
100k
1%
*OPTIONAL
C3*
0.1µF
2955 F10
Figure 10. PowerPath Control with 6V Undervoltage Detect
2955fa
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15
LTC2955
APPLICATIONS INFORMATION
mitigate the effect of the board leakage, a 10k resistor to
VIN is recommended (see Figure 12).
LTC2955-1/
LTC2955-2
VIN
VIN
VLDO
R7
10k
900k
The maximum operating current of the LTC2955 is less
than 3µA, creating an insignificant voltage drop across
the resistor. Using a capacitor value of 10nF provides
sufficient filtering for most applications and larger values
can actually diminish its effectiveness.
PB
0.8V
>2µA
GND
EXTERNAL BOARD
LEAKAGE CURRENT
2955 F12
IF EXTERNAL PARASITIC BOARD
LEAKAGE >2µA USE EXTERNAL
PULL-UP RESISTOR
Adding a 10nF capacitor in addition to the 1k resistor can
protect against high voltage input transients that would
exceed the 40V Absolute Maximum Voltage rating of the
VIN pin. These could occur during hot-plugging into a
battery or AC adapter. This can also protect against transients that may appear on the PCB ground during large
ESD strikes at the PB pin.
PINS OMITTED
FOR CLARITY
Applications with Slide Switch
Figure 12. External Pull-Up Resistor on PB Pin
Enhancing VIN Ruggedness
Placing a 1k resistor and a 10nF capacitor at the VIN pin
can be used to enhance ruggedness in some applications.
A 1k resistor in series with the VIN pin allows the LTC2955
to withstand reverse-input voltages. The LTC2955’s VIN pin
is internally clamped to one diode voltage below ground.
In battery operated applications where a battery could be
inserted improperly, this resistor will limit the current and
allow internal clamping to protect the pin.
In some applications, to prevent accidental toggling of the
system power, a slide switch is preferred over a pushbutton. Figure 14 shows a slide switch added in series with
the pushbutton. The user can slide the switch open to
activate the HOLD/LOCK function, where the pushbutton
is disabled. Figure 15 shows a slide switch connected to
the LTC2955 ON pin resistive divider. If the user slides
the switch to the ON position, the LTC2955 ON pin is high
VIN
ON
SEL
HOLD/LOCK
+
VIN
EN
VIN
LTC2955DDB-1
PB
VOUT
GND
NORMAL
2955 F14
LT3060
9V
BATTERY
SHDN
R8
1k
C4
10nF
EN
VIN
LTC2955TS8-1
INT
PB
GND
R1
10k
INT
KILL
KILL
TMR
Figure 14. Using a Slide Switch to Prevent Accidental
Turn-On/Off
µP
VIN
VIN
OFF
ON
2955 F13
EN
SEL
ON
ON
CONT*
0.033µF
LTC2955DDB-1
PB
*OPTIONAL
GND
2955 F15
Figure 13. Enhancing VIN Ruggedness
16
Figure 15. Using a Slide or Toggle Switch to Turn-On/Off
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LTC2955
APPLICATIONS INFORMATION
and the device turns on. If the user slides the switch to
the OFF position, the ON pin voltage drops to 0V and the
LTC2955 activates a turn-off since the SEL pin is high
(DFN package only).
Interface with Switching Regulators
The LTC2955-1 EN pin can be connected directly to most
switching regulator SHUTDOWN inputs. The EN pin high
level output voltage (VEN(VOH)) is typically 4.3V with
VIN >5V, and VEN(VOH) = VIN – 0.5V if VIN
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